This invention relates to hydraulically actuated disc brake calipers, and more specifically, the invention relates to a method and apparatus for consistently retracting a piston after the brakes have been released.
Disc brake calipers are widely used in motor vehicles to slow the vehicle when the brakes are applied. The disc brake caliper includes a hydraulically actuated piston that coacts with spaced apart brake pads. A rotor, which supports a wheel is arranged between the brake pads. The piston is disposed within a bore in a housing. The piston and bore define a hydraulic chamber. One brake pad is coupled to the piston, and a housing flange opposite the piston supports the other brake pad. When a brake pedal is actuated, hydraulic fluid fills the hydraulic chamber and generates a brake pressure which forces the piston outward thereby squeezing the rotor with the brake pads.
After the brake pedal is released, the piston retracts so the rotor may rotate freely between the brake pads. A resilient seal is utilized between the piston and housing to retract the piston when the brake pressure is removed. The seal is received within an annular groove in the housing and has inner and outer diameters. The inner diameter of the seal engages the outer diameter of the piston and the outer diameter is retained within the annular groove. As the piston moves outward when the brake pedal is actuated, the inner diameter of the seal should move with the piston while the outer diameter of the seal remains stationary. When the brake pressure is removed, the seal should retract the piston.
However, with prior art disc brake calipers, the seal may fail to retract the piston, which permits the brake pads to drag on the rotor and reduce fuel economy. The brake pressure within the hydraulic chamber may reach 1000-1500 psi during hard brake applies, which causes the disc brake caliper to deflect permitting the piston to slide through the seal. Specifically, the piston moves relative to the inner diameter of the seal. As a result, the seal is unable to retract the piston for subsequent brake applies and the brake pads drag on the rotor after the brakes have been released. Therefore, what is needed is a consistent retraction device that retracts the piston and reduces brake pad drag on the rotor thereby increasing fuel economy.
The present invention provides a retraction device for a disc brake caliper having brake pads actuated by hydraulic fluid. The device includes a housing having a bore that defines an axis. A piston is disposed within the bore and is movable along the axis between applied and retracted positions. The piston includes an apply end adapted to coact with the brake pads in the applied position and a hydraulic end opposite the apply end. A hydraulic chamber is defined by the bore and the hydraulic end and contains hydraulic fluid for generating a brake pressure to achieve the applied position. An annular groove is formed in the bore adjacent to the piston, and the annular groove includes a forward angled surface. A resilient seal is disposed within the annular groove for retracting the piston from the applied position to the retracted position. The resilient seal has a first side adjacent the forward angled surface and a second side opposite the first side. A pressure mechanism is arranged adjacent to the second side and is in communication with the hydraulic chamber for generating a retaining pressure to retain the resilient seal against the forward angled surface in response to the brake pressure. The pressure mechanism releases the retaining pressure to permit the resilient seal to retract the piston when below the brake pressure.
The present invention also provides a method of retracting a piston within a disc brake caliper. The method includes the steps of applying brake pressure to the piston and applying a retaining pressure to retain a resilient seal that is in engagement with the piston against an angled surface. The method also includes the steps of removing the brake pressure from the piston and removing the retaining pressure to retract the piston with the resilient seal.
Accordingly, the present invention provides an apparatus and method of consistently retracting the piston and reducing brake pad drag on the rotor thereby increasing fuel economy.